The aim of our program is to apply new non-linear Electron Paramagnetic Resonance spin response techniques to the characterization of well-defined biological systems such as: (1) the membrane associated protein D-beta-hydroxybutyrate dehydrogenase which is functional only when in a specific lipid environment and (2) the purified Ca ions pump protein of rabbit sacroplasmic reticulum which can be reconstituted to form functional lipid containing vesicles. These two experimental systems provide an optimal framework for the investigation of lipid and protein motional interaction in membranes. We can control the parameters of lipid composition and lipid-to-protein ratio in these reconstituted functional systems and we have already characterized biological activity as a function of these parameters. Saturation transfer EPR technology and computer based numeric signal averaging and signal cross correlation techniques will be used to study molecular motion in these membrane systems. We will correlate the measured parameters of molecular motion with biological function. We hope to develop an interactive spectral simulation system which will facilitate the interpretation of the motional aspects of the spectra by providing a rapid and covenient means of iteratively matching the simulated and experimental results. In this way we hope to provide a means of evaluating the structural significance of the spectra of spin-labelled lipoproteins and membranes by the analysis of the effects of motion on the non-linear spin response of paramagnetic probe.